1. Field of the Invention
The present invention relates to conductive particles, as well as an anisotropic conductive film, bonded structure, and bonding method using the conductive particles.
2. Description of the Related Art
To connect circuit members to each other, such as a connection between a liquid crystal display device and a tape carrier package (TCP), a connection between a flexible printed circuit (FPC) and a printed circuit board, or a connection between a FPC and a printed circuit board, a circuit connecting material (e.g., anisotropic conductive adhesive), in which conductive particles are dispersed in an adhesive, is used. In recent years, when a semiconductor silicon chip is mounted on a substrate, in order to connect circuit members to each, so-called “flip chip mounting” is employed in which the semiconductor silicon chip is directly bonded face down on the substrate without using a wire bond. In this flip chip mounting, circuit connecting materials, such as an anisotropic conductive adhesive, are used for connecting circuit members to each other.
The anisotropic conductive film generally contains a binder resin and conductive particles. As the conductive particles, for example, nickel (Ni) based conductive particles have been popular as hardness thereof is high, and a cost can be reduced compared to use of gold (Au) based conductive particles.
As examples of the nickel-based conductive particles, there are (i) conductive particles each of which has a resin core particle, a nickel plating layer formed on a surface of the resin core particle, and protrusions on a surface of the conductive particle (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2006-302716, Japanese Patent (JP-B) No. 4235227, and JP-A Nos. 2006-228475, 2007-173075), and (ii) conductive particles in each of which surfaces of easily oxidized nickel core particles are plated with gold (see, for example, JP-A No. 2004-238738).
The protrusions formed on surfaces of the conductive particles (i) can realize a firm connection because pressure is concentrated on contact points between the protrusions and a circuit member when circuit members are pressure bonded for conductive connection. Moreover, as the protrusions break the oxidized coating on a surface of the electrode, the connection reliability can be improved.
Since the conductive particles (i) uses a resin, which has elastic deformation characteristics, as a material of the core particles, however, there are cases where the conductive particles (i) cannot break an oxide coating formed on a surface of an electrode of a circuit member depending on the hardness of the circuit board, even though the conductive particles (i) have protrusions on the nickel plating layers. Therefore, there is a problem that the connection reliability is low.
Moreover, in the conductive particles (ii) in which surfaces of the nickel core particles are plated with gold, the gold formed on the surface has low Mohs hardness, i.e., 2.5. Therefore, there are cases where the conductive particles (ii) cannot break an oxide coating on a surface of an electrode of a circuit member, which reduces connection reliability.